Activated uranium dioxide and processes of producing the same



Patented May 11, 1954 ACTIVATED URANIUM DIOXIDE AND PROC- ESSES OF PRODUCING THE SAME Milton J. Polissar, San Francisco, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission No Drawing. Application July 13, 1943, Serial No. 494,448

3 Claims.

The present invention relates to activated uranium dioxide and processes of producing the same.

Commercial U02 is ordinarily in the form of a chocolate brown powder and is very stable in ordinary air at room temperature. In fact, this product exhibits no tendency to oxidize in ordinary air until it is heated to a temperature of the order of 100 0., under which conditions it is oxidized to the black oxide U308 in accordance with the following reaction:

This reaction is only normal in view of the fact that commercial U02 is ordinarily prepared by the reduction of U02 or U302 with H.

While this great stability of commercial U02 considerably simplifies the problem of storage prior to use it is believed to represent a surface characteristic that is responsible for the stability of this product in ordinary air at room temperature. Also, it is thought that this characteristic of commercial U02 accounts primarily for the moderate rate of chlorination of this product with 0014 vapor at an elevated temperature in order to produce U014, as disclosed in the copending application of James M. Carter, Serial No, 490,293, filed June 10, 1943, in which the following specific reactions are carried out:

The present invention is predicated upon the discovery that U03 may be reduced with natural gas, consisting essentially of H4, in order to prepare U02 and that this product is highly active with respect to commercial U02 prepared by any known process, including the reduction of U03 and U302 with H, which represents the most feasible commercial process. It is surmised that this activated form of U02 has a surface condition that is responsible for its increased activity, but since this fact has not been definitely established it may prove to be a characteristic of the product engendered entirely by virtue of its preparation utilizing natural gas as a reduction agent. In any case, this activated form of U02 exhibits characteristics so radically different from conventional forms of U02 that it cannot be maintained that these two forms of this compound are identical except in chemical formula.

For example, ordinary U02 exhibits no tendency to oxidize in ordinary air at room temperature; whereas the activated form of U02 is characterized by rapid oxidation under these condi- 2 tions. Similarly, ordinary U02 may be chlorinated with 0014 vapor to produce U014 only at a moderate rate; whereas the activated form of U02 may be rapidly chlorinated with 0014 vapor to produce the product mentioned.

Accordingly, it is an object of the invention to provide the activated form of U02.

Another object of the invention is to provide the highly active form of U02 which is characterized both by rapid oxidation in ordinary air at room temperature and by rapid chlorination with 0014 vapor at an elevated temperature.

Another object of the invention is to provide the activated form of U02 which is prepared by reduction of U03 with natural gas, consisting essentially of 0H4.

A further object of the invention is to provide an improved process of producing U02 utilizing natural gas as a reducing agent.

A further object of the invention is to provide an improved process of producing U02 which employs the reduction of U03 with natural gas.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification.

In accordance with the present invention, a suitable Kjeldahl flask is first swept clear of air by employing a stream of nitrogen which has been passed through a drying agent such as H2S04. A suitable charge of U03, the bright red powder, is then placed in the flask; the flask is stoppered; and the charge is subjected to a stream of natural gas consisting essentially of CR4. Preferably, the natural gas is first passed through a drying agent such as H2804 before it is admitted through a first tube extending through the stopper into the flask, in order positively to insure that no moisture is transferred to the charge. The flask is then heated by a suitable heater, whereby the charge is reacted. The reaction gases produced, together with the excess natural gas, are conducted from the flask through a second tube extending through the stopper. More particularly, the charge is heated to a temperature within the range 400 to 500 0., the temperature of the charge being maintained as close to 450 0. as is practicable. When the charge of U03 is thus heated to a temperature within the range mentioned in the presence of a stream of natural gas it is reduced to U02 in accordance with the following reaction:

4UO3 +CH4 4UO2+ CD2+ 2H2O The reaction gases, including 002 and water vanor, are swept from the flask by the excess natural gas, whereby the U02 produced is substantially completely dry and is in the form of a chocolate brown powder. The process is continued until the charge of U03 is completely converted into U02.

Example When the process is carried out employing a charge of U03 of 100 grams the charge is substantially completely reduced to produce approximately 94 grams of the product U02 in approximately one hour under the conditions specified.

After the charge of U03 has been converted into the product U02 the flask is detached and transferred to a dry cabinet containing an atmosphere of CO2 before it is opened in view of the fact that the product U0 is highly reactive with ordinary air at room temperature, the product being capable of ready oxidation and evolving a great deal of heat when exposed to ordinary air. The product U02 is bottled in an atmosphere of 002 or in a vacuum and sealed for future use. The product U02 so produced is particu larly Well suited for use in the process of producing U014 disclosed in the previously mentioned copending application of James M. Carter.

While analyses clearly indicate that this product produced in accordance with the present process has the chemical formula U02 it is apparent that this product is in a highly active state and, in fact, constitutes activated U02. This fact is readily evidenced by the special properties of the activated U02 as contracted with the ordinary properties of commercial U02. For example, this activated U02 is rapidly oxidized in ordinary air at room temperature, producing U308; whereas commercial U02 exhibits no oxidation in ordinary air until it is heated to a temperature of the order of 100 C. Also, this acti vated U02 may be rapidly chlorinated with CCli vapor to produce U014, as disclosed in the previously mentioned copending application of James M. Carter; whereas commercial U02 may be so chlorinated only at a moderate rate.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. The process comprising reducing U03 with natural gas at a temperature Within the range 400 to 500 0., whereby pyrophoric U02 is produced.

2. The process comprising reducing U03 with CH; at a temperature within the range 400 to 500 0., whereby pyrophoric U02 is produced.

3. The process comprising reducing U03 with a methane-containing gas at a temperature within the range 400 to 500 0., whereby pyrophoric U02 is produced.

References Cited in the file of this patent der anorganischen Chemie, vol. IV, part 1, second half, page 907. Verlag von S. Hirzel, Leipzig (1921). Div. 59.)

Candea, The Methane Gas of Rumania, Chemical Abstracts, vol. 32, page 9447 (1938).

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3. THE PROCESS COMPRISING REDUCING UO3 WITH A METHANE-CONTAINING GAS AT A TEMPERATURE WITHIN THE RANGE 400* TO 500* C., WHEREBY PYROPHORIC UO2 IS PRODUCED. 